Gas separation



Oct. 24, 1939. 1.. H ORVITZ GAS SEPARATION Filed Feb. 8, 1937 1.50uonv/r'z INVENTOR.

mm. awe ATTORNEYS.

Patented Oct. 24, 1939 PATENT OFFlCE GAS SEPARATION Leo Horvitz,Houston, Tex assignor, by mesne assignments, to E. E. Rosalre, Houston,Tex.

Application February 8, 1937, Serial No. 124,652

7 Claims. (Cl. 62-1755) ponents of gaseous mixtures by stages, theresi-- due of the desired gas or gases from a preceding stage beingpartially removed in a succeeding stage or stages.

It is also an object to separate desired com ponents from a gaseousmixture by freezing and 15 collecting portions 01 such components ineach of successive stages.

A further object is to effect separation by successive stages of desiredcomponents of a gaseous mixture by freezing of certain components 20 inthe respective stages and r'evaporizing any residue of the gas passingbetween the stages in solid form.

Other and further objects, together with the foregoing, will be apparentfrom the following 25 description taken in connection with the drawingin which:

Fig. 1 is an illustration of the apparatus employed in practicing .theprocess of the invention.

' Figs. 2 and 3 are alternative forms of the 30 specific embodiment ofthe invention illustrated in Fig. 1.

In the study of gases and in many industrial operations it is desirableor necessary to completely remove a given component or components 35forming gaseous mixtures. Likewise, it is frequently desirable toascertain the amount of a given gas in a gaseous mixture wherein the gas,to be measured is of an extremely low concentration. In' either casedimculty has been ex- 40 perienced in effectively separating thecomponent or components from the gaseous mixture.

The method frequently practiced is that of separation by fractionalfreezing wherein the gas undergoing treatment is subjected to a lowtemperature whereby a certain component or components are liberated andcollected by freezing.

It has been assumed heretofore that if adequate trap area exists, whenseparating gases by fractional freezing, the only limitation to completeremoval of a given gaseous component was the vapor pressure of thatcomponent at the temperature of the freezing bath. Further, if re movalwere not complete it has been supposed 55 that a reduction oftemperature or increase in trap area would accomplish the more completeremoval.

Recently conducted experiments show that complete removal has notfollowed from an in,- creased area of trap, even at temperatures per- Imitting only a negligible vapor pressure of the material frozen out;This invention is concerned primarily withthe complete removal of carbondioxide from a gaseous mixture prior to a quantitative analysis. It isto be understood, however, that the invention is not limited Ito theremoval of carbon dioxide, this particular gas being referred to by wayof illustration only. In pracdoing the invention a trap, or tubularcoil, immersed in liquid air at temperatures between --180' and 190centigrade is used. By this procedure carbon dioxide is frozen out to asnow, the solid phase, with a vapor pressure less than l l0- or even ix10- millimeters of mercury. Theoretically, this treatment shouldcompletely remove the carbon dioxide. However, careful analysis showsthat appreciable traces pass through the trap along the gaseous com.-ponents from which the carbon dioxide should have been separated.

It has been found that by means of the present invention completeremoval of carbon dioxide from a gaseous mixture can be accomplished,the method of and the apparatus for practicing the invention beingillustrated in the drawing and 80 the description now presented.

Fig. 1 shows successive traps, generally designated as H, l2 and ii, inflow line I, through which the gaseous mixture to be processed ispassed. This flow line I is illustrated as a glass tube which may be ahollow member of any suit able material and configuration. The trapportions Ii, 12 and it are immersed in liquid air or other freezingmedium II, I! and 43 in vacuum bottles SI, 32, 33, respectively.Intervening the successive freezing stages are reheating or reyaporizingstages 2|, 2 2 which are employed to revaporize any frozen materialblown or carried past the preceding trap or traps. Any suitable mode ofeffecting desired heating in the revapor- 45 izing stages 2|, 22,-may beresorted to, as is well known in the art, and the flow line i in thesestages may assume any desired configuration to obtain the necessaryrevaporization of the solids passing through this portion of the flowline.

In the modifications shown in Figs-2 and 3, the construction is suchthat a single vacuum bottle 3| is used for the freezing medium H and allthe traps are immersed in this single body of liquid.

In Fig. 2 but two traps II and I! are provided for extracting heat fromthe processed gases and for collecting the solidified components of thegases. These traps are especially constructed in order to present alarger area to the freezing medium ll whereby greater elfectiveness inthe fractional freezing accrues. This specific construction comprisesthe provision of spiral rises i4 and I 5 about the downwardly extendinglegs l6 and I! of the inlet and outlet portions of flow line I.Similarly, the revaporizing stage 2| is spiralled as at 23 to enhancethe application of heat between the freezing stages to revaporize frozenmaterial carried thereto by the preceding trap.

The modification shown in Fig. 3 is similar to the form illustrated byFig. 1 but comprehends a more compact arrangement of component partswhereby traps ll, I2 and iii are immersed in a single body of freezingliquid ii in vacuum bottle 3|. This compact arrangement also providesjuxtaposition of the revaporizing stages 2!, 22 whereby more compactheating means or a single heating unit may be utilized for providing thenecessary heat for revaporization of the frozen material passing throughsuccessive freezing stages or traps,

The procedure carried out by the described apparatus is believednecessary because the carbon dioxide snow can be carried appreciabledistances at liquid air temperatures by a stream of gas, even when thegas is moving at a low velocity. A part of the snow fails to settle outor adhere to the walls of the trap, thus remaining suspended in themoving gas stream so that a mere lengthening of the coil or trap wouldfail to increase the effectiveness of the trap except by a negligibleamount. But if the uncollected snow or vapor that would be permitted topass out of the trap, is warmed and changed over to the vapor phase, andthen passed through a subsequent trap, it is readily frozen out andcollected. Depending upon the completeness of removal necessary;additional reheating and freezing stages may be provided.

where Q0 is the amount of a gaseous component to be eliminated whichenters the first of said series of traps a is a constant representingthe fraction blown by or carried through in other than gaseous form b isa constant representing the emciency per unit length of trap l is thelength of trap.

It is evident that the quantity Q is an appreciable fraction of Q0 ifthe constant a is appreciable, regardless of the magnitude of nl.

When reheating stages between freezing traps are used in accordance withthe present invention, it appears that the amount of a given gaseouscomponent, Q, that passes a series 0! n traps is approximated by:

Q=(a+ /l) Qo (2) where Q, a, b, land n are the same as for the precedingequation. Here the value 11 appears as an exponent instead 01' a merefactor, and since (a-i-b/l) is very small compared with unity, the

quantity in parentheses in the equation becomes vanishingly small evenwhen the number of traps n is small.

For example, suppose then for only two traps' which shows that 500 partsper million fails to be trapped. It is therefore apparent that by meansof the process and apparatus of the present invention the effectivenessof separation is greatly increased.

Analyses frequently call for an accuracy of the order of one part, orless, per million so that this invention fills an important need. Inpracticing the present invention it has been found possible to reducethe quantity of carbon dioxide to less than one part per million partsof total gaseous mixture.

While the invention has been specifically described as being applicableto the separation of carbon dioxide from other components of gaseousmixture, the invention is not limited thereto but is also applicable tothe separation of many other substances which can be frozen out, such aswater vapor, ethane, propane, etc. It is also applicable to the methodof separation by liquefaction of such components as water vapor, mercuryvapor, alcohols, etc. It is also within the scope of the invention toapply it to those substances which evaporate from a liquid phase, suchas water above 0 C., and other substances which have a liquid phasebetween the solid and gaseous states.

It is also desirable, at times, to separate out two or more componentsfrom a gaseous mixture in a single operation. The invention is veryuseful for this case whenever the two components are amenable to suchextraction. Such cases frequently arise. as for example, when it isdesired to remove carbon dioxide and water vapor.

Furthermore, when two or more constituents are being eliminatedsimultaneously, both may be trapped in the solid state, in the liquidstate, or one or more in the solid state and the others in a liquidstate. Thus, for example, in trapping vapors of ethyl alcohol andmercury, within a given range of temperatures the mercury would betrapped as a solid and the alcohol as a liquid.

What is claimed is:

l. The method of removing carbon dioxide from a gaseous mixture whichcomprises the steps of reducing the carbon dioxide to a solid phase oflow vapor pressure, collecting such solid, revaporizing that portionwhich is carried past the first solidifying stage, and subsequentlyresolidifying. and collecting the portion which was carried over.

2. The method of removing a component from a gaseous mixture whichcomprises the step of reducing that component to a solid phase of lowvapor pressure and collecting such solid, repeating said reducing andcollecting step, and between said repeated steps revaporizing such solidas has failed to be collected in the preceding step.

3. Means for removing carbon dioxide from a gaseous mixture comprising aplurality of means operating successively for solidii'ying andcollecting the carbon dioxide, and intervening means for vaporizing suchcarbon dioxide as has been blown or carried through the previoussolidifying and collecting means.

4. Means for removing a gaseous component from a gaseous mixturecomprising a plurality of means operating successively ior solidifyingor liquetying and collecting said component, said means comprisingsuccessive traps and cooling means therefor and means intermediatesuccessive traps for revaporlzing such part of said component which hasbeen blown or carried through the previous collecting means.

5. Means for removing a component from a gaseous mixture comprising aplurality 01 means operating successively for solidifying and collectingsuch component, and intervening means for revaporizing such solid as hasbeen blown or carried past the previous solidifying and collectingmeans.

6. The method or removing a component from a gaseous mixture comprisingthe steps of, sub- Jecting the mixture to a temperature at which thecomponent is liquefied and exerts a low vapor pressure, collecting theliquid so formed, reheating the remaining gas to revaporize anycondensed liquid carried past the liqueiying stage, and subjecting theremaining mixed gases to a temperature at which any of the componentcarried past the first liquetying stage is liquefied and collected.

7'. 'lhe method of removing components from a gaseous mixture comprisingthe steps of sub- Jecting the mixture to a temperature at which thecomponents are reduced to non-gaseous phases of low vapor pressure,collecting the non-gaseous residues, subjecting the remaining as to areheating step and revaporizlng any non-gaseous residue which is carriedpast the first reducing and collecting step. and again subjecting thegas to a temperature at which any of the components carried past thefirst reducing and collecting stage are reduced and collected.

- LEO HORVIIZ.

DISCLAIMER 2,177 ,139.Leo Horm'ts 24, 1939. Discl Development Company.

Houion, Tex. Gas Summon. Patent dated October aimer filed August 5,1941, by the assignee, Standard Oil Hereby enters this disclaimer tothat part of 1, 2, 6, and which is in the following words, to wit:

Claim 1. and so uently resolidifying and collecting the portion whichwas carried over, except mini as this stepjs carried outin a zoneseparate and distinct from the zone in which the first solidificationstage 1s conducted.

Claim 2. repeating said reducing and collecting step,, except msofar asthis step is carried out in a zone separate and distinct from the zonein which the first reducin and collecting stage is conducted.

laim 6. and subjecting the remaining any of the component carried pastthe first looted, except insofar as this step is carried out in azoneseparate and distinct from store at which mixed gases to a tem 'quefiedand colliquofymg stage is that in which the first liquefying stage iseffected.

Claim 7. and again subjecting the gas to a temperature at which an ofthe components carried past the first reducing and co and colllectingstage are rcdu lected, except insofar as this step, is carried out in azoneseparate and distinct from the zone in which the first reducing andcollecting stage is efl'ected.

[Oficid Gazette August 26, 1941.]

2. The method of removing a component from a gaseous mixture whichcomprises the step of reducing that component to a solid phase of lowvapor pressure and collecting such solid, repeating said reducing andcollecting step, and between said repeated steps revaporizing such solidas has failed to be collected in the preceding step.

3. Means for removing carbon dioxide from a gaseous mixture comprising aplurality of means operating successively for solidii'ying andcollecting the carbon dioxide, and intervening means for vaporizing suchcarbon dioxide as has been blown or carried through the previoussolidifying and collecting means.

4. Means for removing a gaseous component from a gaseous mixturecomprising a plurality of means operating successively ior solidifyingor liquetying and collecting said component, said means comprisingsuccessive traps and cooling means therefor and means intermediatesuccessive traps for revaporlzing such part of said component which hasbeen blown or carried through the previous collecting means.

5. Means for removing a component from a gaseous mixture comprising aplurality 01 means operating successively for solidifying and collectingsuch component, and intervening means for revaporizing such solid as hasbeen blown or carried past the previous solidifying and collectingmeans.

6. The method or removing a component from a gaseous mixture comprisingthe steps of, sub- Jecting the mixture to a temperature at which thecomponent is liquefied and exerts a low vapor pressure, collecting theliquid so formed, reheating the remaining gas to revaporize anycondensed liquid carried past the liqueiying stage, and subjecting theremaining mixed gases to a temperature at which any of the componentcarried past the first liquetying stage is liquefied and collected.

7'. 'lhe method of removing components from a gaseous mixture comprisingthe steps of sub- Jecting the mixture to a temperature at which thecomponents are reduced to non-gaseous phases of low vapor pressure,collecting the non-gaseous residues, subjecting the remaining as to areheating step and revaporizlng any non-gaseous residue which is carriedpast the first reducing and collecting step. and again subjecting thegas to a temperature at which any of the components carried past thefirst reducing and collecting stage are reduced and collected.

- LEO HORVIIZ.

DISCLAIMER 2,177 ,139.Leo Horm'ts 24, 1939. Discl Development Company.

Houion, Tex. Gas Summon. Patent dated October aimer filed August 5,1941, by the assignee, Standard Oil Hereby enters this disclaimer tothat part of 1, 2, 6, and which is in the following words, to wit:

Claim 1. and so uently resolidifying and collecting the portion whichwas carried over, except mini as this stepjs carried outin a zoneseparate and distinct from the zone in which the first solidificationstage 1s conducted.

Claim 2. repeating said reducing and collecting step,, except msofar asthis step is carried out in a zone separate and distinct from the zonein which the first reducin and collecting stage is conducted.

laim 6. and subjecting the remaining any of the component carried pastthe first looted, except insofar as this step is carried out in azoneseparate and distinct from store at which mixed gases to a tem 'quefiedand colliquofymg stage is that in which the first liquefying stage iseffected.

Claim 7. and again subjecting the gas to a temperature at which an ofthe components carried past the first reducing and co and colllectingstage are rcdu lected, except insofar as this step, is carried out in azoneseparate and distinct from the zone in which the first reducing andcollecting stage is efl'ected.

[Oficid Gazette August 26, 1941.]

